> Based on which signs or hypothetical scenario are you imagining that this whole systems turns back on itself and breaks?
This is an easy one to answer. Proof of work as implemented in bitcoin is the largest, weirdest incentivized, most highly distributed preimage attack [1] ever run against any hash algorithm that we know of in human history. The history of hash algorithms suggests that humanity has yet to invent a perfect hash algorithm (whether or not you agree that perfect hash algorithms are even mathematically theoretically possible), which makes it very clearly a matter of "when" the distributed preimage attack succeeds in breaking the hash algorithm altogether rather than "if".
> the market overwhelmingly disagrees
The "market" isn't by definition a rational actor and may just be a mob swept up into fervor. Ponzi schemes in general prey on weaknesses in a market's mentality or emotionality to follow bad long term advice for short term gains. (That example should work whether or not you also agree that bitcoin-style mining difficulty is also directly a unique modern variant of a Ponzi scheme.)
Don't you think we have other problems too if Sha-2 is broken? I'm going to assume that you aren't worried about the numerous other applications where this scenario would be catastrophic?
In any case, this scenario has very well been accounted for. The Bitcoin network can fork its consensus rules when such drastic requirements require it. Such as to a different hashing algorithm, and snapshotting of its previous state.
> Ponzi scheme
This goes back to square one, which is that in the absence of understanding the value of bitcoin, a scheme is the only logical explanation.
We are now sitting at 10 years and $XXB ponzi scheme. Perhaps one of greatest schemes in history? Maybe it will unravel in the next 10? Time will tell.
> Don't you think we have other problems too if Sha-2 is broken? I'm going to assume that you aren't worried about the numerous other applications where this scenario would be catastrophic?
It is exactly this reason I find bitcoin incredibly scary. The catastrophe that happens if bitcoin "succeeds" in breaking SHA-2 is directly part of why I think Proof of Work is at best a waste of processing power, and at worst a catastrophe we are watching in real time.
> In any case, this scenario has very well been accounted for. The Bitcoin network can fork its consensus rules when such drastic requirements require it. Such as to a different hashing algorithm, and snapshotting of its previous state.
Which again is my point earlier: forks are natural parts of how bitcoin operates and directly a part of the underlying data structures. It doesn't exist without forks. You couldn't build bitcoin without forks. It isn't considered likely it would continue to exist in the future past certain points (including catastrophic ones) without forks. So the distinction of which fork is the "one true fork" is a political economics game, not a technical distinction in any way.
This is an easy one to answer. Proof of work as implemented in bitcoin is the largest, weirdest incentivized, most highly distributed preimage attack [1] ever run against any hash algorithm that we know of in human history. The history of hash algorithms suggests that humanity has yet to invent a perfect hash algorithm (whether or not you agree that perfect hash algorithms are even mathematically theoretically possible), which makes it very clearly a matter of "when" the distributed preimage attack succeeds in breaking the hash algorithm altogether rather than "if".
> the market overwhelmingly disagrees
The "market" isn't by definition a rational actor and may just be a mob swept up into fervor. Ponzi schemes in general prey on weaknesses in a market's mentality or emotionality to follow bad long term advice for short term gains. (That example should work whether or not you also agree that bitcoin-style mining difficulty is also directly a unique modern variant of a Ponzi scheme.)
[1] https://en.wikipedia.org/wiki/Preimage_attack